In 2201, humanity has colonized the reaches of space, but an unexpected threat emerges when a mysterious cyborg army called Chron attacks Earth and its settlements from deep space. The true origin of these mechanical invaders remains a puzzle at first, though evidence gradually points to a darker history—they are the remnants of an exploration mission dispatched by Earth a century before, now returning with unknown intentions. As Rex, a decorated commander of the Earth Defense League, you pilot an Assault Suit, a towering combat machine designed to protect humanity's future. Your mission spans multiple theaters of war, from the ice moons of Jupiter to orbital battles and ground assaults on Earth itself, as you work to uncover what transformed explorers into enemies and discover the purpose behind Chron's relentless campaign.